1. Field of the Invention
The present invention generally relates to projecting a two-dimensional image in color while maintaining low power consumption, high resolution, miniature compact size, quiet operation and minimal vibration and, more particularly, to increasing the symmetry of pixels which comprise the image.
2. Description of the Related Art
It is generally known to project a two-dimensional image comprised of pixels on a screen based on a pair of scan mirrors which oscillate in mutually orthogonal directions to scan a laser beam from a laser over a raster pattern. The laser beam is incident as a beam spot on one of the mirrors, for example, a horizontal scan mirror, to sweep the beam spot along a horizontal scan line extending along a horizontal scan direction. The horizontal scan line is incident on the other of the mirrors, i.e., a vertical scan mirror, to sweep the scan line along the vertical direction, thereby creating the raster pattern. Turning the beam spot on by energizing the laser, as the beam spot is swept along each scan line, causes selected pixels in each scan line to be illuminated and rendered visible, while turning the beam spot off by deenergizing the laser causes the remaining pixels to be non-illuminated. The illuminated and non-illuminated pixels comprise the image being projected.
Although generally satisfactory for their intended purpose, the known image projection arrangements project the image with limited resolution, typically less than a fourth of video-graphics-array (VGA) quality of 640×480 pixels and, moreover, the pixels are asymmetrical, thereby degrading the image. The size of an individual illuminated pixel depends, among other factors, on the initial size of the beam spot (when it is turned on) incident on the horizontal scan mirror and the motion of the beam spot as the horizontal scan mirror sweeps the beam spot. In other words, the size of the illuminated projected pixel is larger than the initial size of the incident beam spot, as considered along the horizontal scan direction. For example, if the incident beam spot on the horizontal scan mirror were circular in cross-section, then the corresponding projected pixel would be elliptical in cross-section with the larger axis aligned along the horizontal scan direction. The projected pixel is thus “stretched” out along the horizontal direction, but is not so stretched along the vertical direction, thus leading to a poorly displayed image comprised of asymmetrical pixels.